The present inventions relates generally to the construction and use of medical monitoring devices. More particularly, the invention relates to an ambulatory monitoring device for measuring gastric acid reflux in a patient.
Gastric acid reflux is a common human ailment arising from the backwash or "reflux" of stomach acid into the esophagus. Mild reflux or "heartburn" is a very common condition experienced by nearly everyone at one time or another. However, prolonged or repeated bathing of the esophagus with gastric acid leads to gastroesophageal reflux disease or "GERD." Left untreated, this condition may progress to esophagitis, esophageal ulceration, stricture, and malignant tumor formation.
Early diagnosis of reflux is an important aspect in the successful treatment and prevention of GERD. While many patients experience heartburn-like symptoms during reflux, it is difficult to quantify the degree of reflux from symptoms alone. Symptoms may even be absent in some patients. Moreover, since reflux mimics cardiac chest pain (and vice versa), the physician must confirm that the symptoms are in fact due to reflux. Thus, in evaluating the patient suspected of having reflux, it is necessary to assess the presence and severity of reflux, nature of refluxant, presence and severity of esophagitis, and pathophysiology of reflux.
The lower esophageal sphincter (LES), in conjunction with the anatomical configuration of the gastroesophageal (G-E) junction, forms an anti-reflux "valve" between the stomach and the esophagus. The LES cannot be identified anatomically as anything but the lower end of the esophagus, i.e., it is virtually indistinguishable from the muscle of the esophagus. Nevertheless, the circular muscle there remains tightly constricted between swallows, thereby preventing the regurgitation of gastric contents into the esophagus. Reflux occurs when the LES-gastric pressure gradient is lost, for example, by a transient or sustained decrease in sphincter tone or by increased intragastric pressure.
Since the mid 1970's, several diagnostic tests have been devised to measure the occurrence of reflux occurring in a patient by measuring acidity above the LES. A simple way of documenting reflux is to first insert a pH probe down the nose or mouth towards the stomach. A low pH reading is observed when the probe reaches the acid-rich stomach. Next, the probe is slowly retracted while monitoring the pH for change. As the probe enters the lesser acidic esophagus, a rise in pH is detected. This location is assumed to be the LES and measurements are taken. Unfortunately, this assumption is more often wrong than right. Thus, the results obtained are unreliable.
A more accurate method of measuring reflux is to place a pH probe a certain or specified distance above the LES. Scoring criteria (for example, the Johnson and DeMeester score) have been established to grade the severity of the reflux based on this technique. However, the technique is reliable only if the pH probe is properly positioned at a known location--a certain distance above the LES. Since the LES is not a clearly defined anatomical structure, it is preferably located by pressure measurements to detect the "high pressure zone" (HPZ). The HPZ location is considered to be the anatomical site of the LES. Thus, a prerequisite to accurately measuring reflux in a patient is determining the correct location of the HPZ.
Locating the HPZ can be done as part of a diagnostic esophageal motility study. Using standard esophageal intubation technique, a probe equipped with a pressure transducer is inserted into the nose or mouth (naso- or oro-esophageal intubation), advanced through the pharynx and esophagus until it reaches the stomach. The pressure transducer, which converts pressure readings into electrical signals, can be recorded on a strip chart recorder.
While observing the recorder, the operator, such as a physician or technician, slowly withdraws the probe from the stomach. As the transducer traverses the HPZ a rise in pressure is noted. At this instance, the depth of the probe is noted. Then the pressure transducer probe is removed from the patient. Next, a pH probe is inserted and advanced to a depth of 5 cm above the LES. The pH probe can be connected to a data collection box or "data logger" which the patient wears for a 24-hour collection period. During this time the pH is frequently measured (typically at 5 seconds intervals) with the values stored in memory. Upon completion of the test, the probe is removed and the data are analyzed.
While this technique is an improvement over prior procedures, it still has several disadvantages. Most reflux patients have low or non-existent LES tone (LES incompetence), thus this technique is unable to accurately determine the LES for these patients. The technique also requires two intubations, i.e., the placement of two probes in succession. Most patients find intubation uncomfortable but tolerable. Some patients, however, such as those with hyperactive gag reflexes, exhibit severe discomfort with intubation. In this latter group, initial intubation is difficult and repeated intubation is impossible. Furthermore, the technique employs hardware which is cumbersome, expensive, and complicated--requiring trained technicians or nurses to operate them--thus making the test expensive.
What is needed is a system which provides a cost effective and accurate method to monitor reflux with minimum inconvenience to the patient. The present invention fulfills these and other needs.